1. Field of the Invention
This application is related to copending U.S. Pat. application Ser. No. 599,592, filed Oct. 18, 1990, now U.S. Pat. No. 5,073,614 and assigned to the same assignee as herein.
This invention relates to gelled acidizer compositions, particularly for use in matrix or fracture acidizing operations to stimulate oil and gas wells, and even more particularly, to such compositions which contain strongly swellable, moderately crosslinked polyvinylpyrrolidone as the gelling agent therein.
2. Description of the Prior Art
Various polymers have been used as gelling agents for acids used to stimulate oil and gas wells with bottom hole temperatures ranging from 100.degree. to 300.degree. F. The complete spectrum of hydrochloric acid concentrations (1-28%) have been gelled for matrix or fracture acidizing treatments in limestone, dolomite, or other calcacareous formations. However, it is necessary, and often lacking, in such acid gelling agents, to maintain a stable, high viscosity for controlling acid fluid leak-off to the formation and retardation of the acid reaction rate with the acid-soluble formation. Furthermore, post-treatment stability in high concentrations of calcium ion is very important in the spent acid fluid. Polyacrylamide-based acid gelling agents fail in this respect because they produce formation-damaging precipitates. It is preferred, instead, that the gelling agent thin out with pad fluids or connate water to a lower viscosity and provide post-treatment clean-up of formation fines and silts which can cause formation damage and rapid production declines.
Accordingly, it is an object of the present invention to provide a novel gelled acidizer composition.
Another object of the invention is to provide a novel gelled acidizer composition useful in matrix or fracture acidizing operations to stimulate oil and gas wells.
Still another object is to provide such compositions which are useful over a wide acid concentration range, and wide temperature range, and which provides a high viscosity at relatively low concentrations of the gelling agent.
These and other objects and features of the present invention will be made apparent from the following more particular description of the invention.